Add support for Rails 6.0 to ViewContext::BuildStrategy (#866)

* Add support for Rails 6.0 to `ViewContext::BuildStrategy`

In Rails 6.0 the API for `ActionView::Base.new` is changing.
`ActionView::Base.new` now take arguments [1], otherwise you
will see the following deprecation warning:

```
DEPRECATION WARNING: ActionView::Base instances should be constructed with a lookup context, assignments, and a controller.
```

[1] e17fe52e0e

`ViewContext::BuildStrategy::Fast` does not have lookup context, so use `empty`
method instead of `new` to build instance.

* Bump a Rails version of dummy application

Also bump a sqlite version because Rails 6.0 requires upper sqlite
1.4.0.

* Add `ApplicationController` to dummy application

Because Action Text expects `ApplicationController` exists.
Ref: https://github.com/rails/rails/issues/35749#issuecomment-525083643

* Test against Rails 6.0 that only supported Ruby versions

Gemfile

@@ -3,7 +3,11 @@ source "https://rubygems.org"
 gemspec
 
 platforms :ruby do
-  gem 'sqlite3', '~> 1.3.6'
+  if RUBY_VERSION >= "2.5.0"
+    gem 'sqlite3'
+  else
+    gem 'sqlite3', '~> 1.3.6'
+  end
 end
 
 platforms :jruby do
@@ -11,5 +15,9 @@ platforms :jruby do
   gem "activerecord-jdbcsqlite3-adapter"
 end
 
-gem "rails", "~> 5.0"
+if RUBY_VERSION >= "2.5.0"
+  gem "rails", "~> 6.0"
+else
+  gem "rails", "~> 5.0"
+end
 gem "mongoid", github: "mongodb/mongoid"

lib/draper/view_context/build_strategy.rb

@@ -12,7 +12,7 @@ module Draper
         end
 
         def call
-          view_context_class.new
+          view_context_class.respond_to?(:empty) ? view_context_class.empty : view_context_class.new
         end
 
         private

spec/dummy/app/controllers/application_controller.rb

@@ -0,0 +1,2 @@
+class ApplicationController < ActionController::Base
+end